Presensitized lithographic plate with two differentially spectrally sensitized layers separated by a novolak resin

ABSTRACT

THE APPLICATION DESCRIBES A COMPOSITE PRESENSITISED LITHOGRAPHIC PLATE WHICH COMPRISES A HYDROPHILIC-SURFACE SUPPORT BASE AND COATED THEREON, IN ORDER, A FIRST LIGHTSENSITIVE LAYER WHICH IS AN ADHERENT LIGHT-SENSITIVE LAYER OF THE TYPE WHICH IS CAPABE OF BEING USED AS THE LIGHTSENSITIVE LAYER IN A NEGATIVE-WORKING PRESENSITISED LITHOGRAPHIC PLATE, AN INTERMIEDIATE PROTECTIVE LAYER OR LAYERS, THE LAYER OR IF THERE IS MORE THAN ONE LAYER, THE LAYER WHICH IS NEAREST TO THE SAID FIRST LAYER, BEING A NONHARDENABLE RESIN OF THE CONDENSED PHENOL-CARBONYL COMPOUND TYPE, AND A SECOND LIGHT-SENSITIVE LAYER WHICH IS A SILVER HALIDE EMULSION LAYER.

United States Patent ()flice 3,567,445 Patented Mar. 2, 1971 3,567,445PRESENSITIZED LITHOGRAPHIC PLATE WITH TWO DIFFERENTIALLY SPECTRALLYSENSI- TIZED LAYERS SEPARATED BY A NOVOLAK RESIN Lawrence Atkinson,Leonard Roy Brooker, and Brian Ronald David Whitear, llford, Essex,England, assignors to Polychrome Corporation, Yonkers, N.Y. No Drawing.Filed Oct. 20, 1967, Ser. No. 676,713 Claims priority, application GreatBritain, Oct. 28, 1966,

1 48,491/ 66 Int. Cl. G03f 7/02 US. Cl. 96-33 14 Claims ABSTRACT OF THEDISCLOSURE The application describes a composite presensitisedlithographic plate which comprises a hydrophilic-surface support baseand coated thereon, in order, a first lightsensitive layer which is anadherent light-sensitive layer of the type which is capable of beingused as the lightsensitive layer in a negative-working presensitisedlithographic plate, an intermediate protective layer or layers, thelayer or if there is more than one layer, the layer which is nearest tothe said first layer, being a nonhardenable resin of the condensedphenol-carbonyl compound type, and a second light-sensitive layer whichis a silver halide emulsion layer.

This invention relates to presensitised lithographic plates and inparticular to such plates which are of camera speed.

The term of camera speed indicates that the presensitised lithographicplate is sufliciently fast in the photographic sense to be used in acamera such as a process camera. Most presensitised lithographic platesat present in use commercially are of contact speed, that is to say thata photographic negative has to be used as an image and this is placed incontact With the plate and the plate is exposed to ultra-violet lightthrough the negative. The consequent need to produce a negative whenusing contact speed plates increases considerably the preparation neededto produce useable plates.

The usual sensitisers for presensitised lithographic plates and inparticular negative working plates are diazo compounds or photosensitivepolymers such as polyvinyl cinnamates but the photographic speed ofthese compounds is too slow for plates sensitised therewith to be ofcamera speed and thus, as previously stated, most presensitisedlithographic plates are of contact speed. The most common sensitiser forphotographic material of camera speed is silver halide and presensitisedlithographic plates have been produced which are silver halidesensitised. However, such plates are comparatively difiicult to processand their printing life, that is to Say the number of prints which canbe taken from them, is not very great.

It is the object of the present invention to provide a presensitisedlithographic plate which is of camera speed but which is comparativelyeasy to process and which is capable of producing a plate of relativelylong printing life.

According to the present invention there is provided a compositepresensitised lithographic plate which comprises a hydrophilic surfacesupport base and coated thereon, in order, a first layer which is anadherent lightsensitive layer of the type which is capable of being usedas the light-sensitive layer in a negative-working presensitisedlithographic plate, an intermediate protective layer or layers, thislayer or if there is more than one layer, the layer which is nearest tothe said first layer,

being a nonhardenable resin of the condensed phenolcarbonyl compoundtype, and a second layer which is a silver halide emulsion layer.

The support base may be any support base commonly used for presensitisedlithographic plates, for example, metal plates such as lightly-grainedaluminium plates, plastics plates such as polyethylene terephthalatewhich has been treated so as to make one surface hydrophilic, paperplates or paper impregnated-with-resin plates.

By light-sensitive layer of the type which is capable of being used asthe light-sensitive layer in a negativeworking presensitisedlithographic plate is meant a layer which can be coated on to the baseand which is sensitive to ultra-violet light and when exposed toultra-violet through a negative in the exposed areas undergoes achemical reaction which renders the exposed areas insoluble. The layeris developed by removing the unexposed unchanged areas thus leaving theinsoluble areas which form a positive image of the original and exposingthe hydrophilic base. The insoluble areas are oleophilic either due tothe fact that the original layer is oleophilic or because on exposure tolight the layer becomes oleo philic. A large number of suchphotosensitive layers have been proposed and used. Exemplary of suchlayers are (a) light-sensitive polymers such as polyvinyl cinnamate,polyvinyl-phosphonic monoesters of chalcones, styrene/ maleic anhydridecopolymers containing a cinnamoyl or chalcone group, vinyl polymerscontaining an aromatic azide group, (b) polymers together with alight-sensitive compound which hardens the polymers when exposed tolight such as gelatin and bichromate, gelatin and diazo compounds,polyacrylate and diazo compounds, vinyl polymers and p-hydroxybenzalacetophenone, styrene/maleic anhydride copolymers and diazo fiuorborate,(c) photopolymerisable mixtures such as acrylamide plus N,N-methylene-bis-acrylamide plus a catalyst, (d) polymeric diazoniumcompounds such as the condensate of 4-diazodiphenylamine andformaldehyde, and (e) lightsensitive compounds which can be coateddirectly on to the support base without any hardenable polymers such asdiazo compounds, diazostilbenes, naphthoquinone diazides, methylenefluorene sulphonic acid and cinnamoyl furfurylidene. These lattercompounds are usually coated on to the support together with anonhardenable resin such as novolak resin to prevent them crystallizingon the support.

The preferred photosensitive layers of the first layer are diazo-resinlayers and in particular the condensation product of4-diazodiphenylamine and formaldehyde and lightsensitive polymerscontaining an unsaturated acyl group such as polyvinyl cinnamate.

The intermediate protective layer or layers are present to prevent thefirst layer hardening the binder of the silver halide emulsion and toprotect the first layer during the processing of the silver halideemulsion.

Particularly useful resins of the condensed phenol-carbonyl compoundtype are the novalak resins which are condensation products of phenoland formaldehyde. These resins have no reactive groups and they are notphotopolymerisable or hardenable by the light-decomposition products ofthe first layer. The presence of an intermediate layer which comprises aresin of the phenolcarbonyl compound type is a particular feature of thepresent invention as most of the resins and other polymeric substancestried hardened onto the exposed first layer. Other polymeric substancestried were not filmforming unless plasticisers were present and theseplasticisers were found to effect the first layer adversely. Otheradvantages of using a phenol-carbonyl compound resin are that silverhalide emulsions adhere directly thereon and the resins are freelysoluble in a number of solvents, e.g., aqueous alkali, ketones andalcohols. However in another embodiment of the invention theintermediate layers may constitute a stripable assembly, in this casethe silver halide emulsion is coated on to a support membrane and thismembrane is anchored to the first layer by a layer of the phenolcarbonyl compound resin. The preferred emulsion support membrane ispolyvinyl alcohol. A particularly useful polyvinyl alcohol is Elvanol73-125 made by the Du Pont Company of the USA.

It is preferred that a gelatino silver halide emulsion is used but otherbinders for the silver halide such as polyvinyl alcohol or polyvinylpyrrolidone may be used. Any type of silver halide emulsion may be useddepending on the original to be reproduced. The most usual original is apositive photographic print, very often in an enlarger, for this a highcontrast silver chloride or chlorobromide emulsion is the most suitable.A direct screened image can be produced by inserting a screen betweenthe original and the plate. For this purpose a lith type emulsion ispreferred. The silver halide emulsion may he colour sensitised to enablecolour separations to be prepared.

According to another aspect of the present invention there is provided amethod of producing a useable printing plate from the presensitisedlithographic plate hereinbefore described which comprises exposing theplate to an original, developing the resultant latent image in thesilver halide layer, fixing out or stabilising the unexposed silverhalide, exposing the plate to an all-over strong light and then removingthe silver halide emulsion and the intermediate layer or layers anddeveloping the resultant positive image of the original in the firstlayer and removing the unexposed light-sensitive material in the firstlayer.

It is preferred that strong light is ultra-violet light. The method ofremoving the silver halide and intermediate layer or layers depends onthe nature of the intermediate layer or layers, and the method ofdeveloping the image in the first layer and removing unexposedphotosensitive material therefrom depends on the sensitiser used in thefirst layer. For example, if the intermediate layer is a single layer ofa novolak resin it is possible to remove the silver halide emulsionlayer and the intermediate layer in dilute alkali solution or the silverhalide emulsion is first removed in hot water, dilute alkali or organicsolvent solution and the intermediate layer is then removed in dilutealkali. However, if the first layer is diazo compound sensitised, dilutealkali reacts with the unexposed diazo. In this case, it is preferred toadd a coupler, which is capable of reacting with a diazo compound toform a dye, to the dilute alkali solution. The coupler reacts with theunexposed diazo compound to form a dye. This dye, which constitutes anegative image of the original is removed either by subsequent treatmentwith an organic solvent, such as the organic solvent used in an imagelacquering solution or if the coupler which is used contains suitablesolubilising groups the dye formed is soluble in dilute alkali and isthus removed in the dilute alkali solution. Alternatively, in some casesit is possible to remove the silver halide emulsion layer, theintermediate layer and the unexposed areas of the first layer bytreatment with an organic solvent such as the solvent used in a combinedplate cleaner lacquering solution, e.g., cyclohexanone.

On the other hand if the intermediate layer or layers constitute astripable assembly this assembly can be removed by dissolving thestripable layer in, for example, dilute alkali or an organic solvent andthen physically removing the emulsion support membrane with the silverhalide coated thereon. Alternatively the emulsion support membrane canbe removed by using physical means alone.

The first layer is developed by treating it with water, dilute alkali,dilute acid or an organic solvent to remove the unexposed areas. Thechoice of solvent depends on the composition of the first layer.Sometimes as hereinbefore described this development step takes place atthe same time as the removal of the intermediate layer or layers.

It is preferred that the image is lacquered to increase its oleophilicproperties and thus prolong the useable life of the plate.

Thus using the composite presenitised lithographic plate of the presentinvention a positive printing plate can be produced from an original byexposing the presensitised plate in a camera, the silver halide emulsionbeing fast enough for this purpose. A silver image is formed which actsas a negative in contact with the light-sensitive first layer. Thislayer is only fast enough to be affected when exposed by theultra-violet or other strong light.

The silver halide emulsion layer and intermediate layer are easilyremoved from the first layer and thus the processing of the compositepresensitised lithographic plate of the present invention can be carriedout without complicated apparatus.

In another embodiment of the present invention wherein the support baseis of transparent material, e.g., when it is cellulose triacetate orpolyethylene terephthalate there has been found a process whereby alaterally correct image may be obtained.

According to this aspect of the present invention there is provided amethod of producing a useable printing plate from the compositepresensitised printing plate hereinbefore described wherein the supportbase is transparent, which comprises exposing the suitably sensitizedsilver halide emulsion layer of the plate to an original through thenoncoated support base with light of a wave-length to which the firstlayer is not sensitive, developing the resultant latent image in thesilver halide layer, stabilising or fixing out the unexposed silverhalide, exposing the plate to an all-over strong light on the silverimage side of the base (thus exposing the first layer through the silverimage), and then removing the silver halide emulsion and theintermediate layer or layers and developing the resultant positive imageof the original in the first layer and removing the unexposedlight-sensitive material in the first layer.

It is preferred that the strong light is ultra-violet light.

By use of this method of exposure and subsequent processing of the platea laterally correct image is obtained without having to use a processcamera with an image converter. As the silver halide emulsion is so muchfaster than the first layer the short initial exposure through the firstlayer does not cause any significant photochemical reaction therein.

The term suitably-sensitised means that the sensitivity of the silverhalide layer is extended so that it is beyond the light absorption ofthe first layer, e.g., diazo-resin layers absorb all the ultra-violetlight and a portion of the blue light.

The following examples will serve to illustrate the invention.

EXAMPLE 1 A negative working faintly grained aluminium platepresensitised with a polymeric diazonium resin was supercoated with a 2%w./v. solution of a novolak resin (believed to be of molecular weightapproximately 1200) in isopropyl alcohol. The smooth coating was driedin a Whirler machine.

A high contrast silver halide emulsion was coated thereon and the evencoating subsequently dried. The composite plate was exposed in a camerato a positive image, the latent silver image so obtained, developed in ametal hydroquinone based developing solution to a high density black,and the nonexposed portions were made light insensitive in a solution ofammonium thiocyanate. There was thus obtained a negative silver image ofthe original.

The plate was given a short exposure to ultra-violet light and the plateprocessed as follows. The silver emulsion and protective interlayer wereremoved by treatment with a solution of sodium hydroxide (0.5 normal)con taining 0.25% W./V. benzoylacetanilide and ethyl alcohol, which atthe same time coupled with the unexposed diazo material to form an azodye. There was thus produced a hardened positive image of the originaland also a negative image composed of azo dye. The plate was theninsensitive to light.-The azo dye was removed and the image protected bylacquering with an emulsion containing essentially an organic solvent,cyclohexanone, an epoxy resin, aqueous gum arabic solution and ananionic wetting agent. The azo dye dissolved in the organic phase andthe resin lacquered the ink receptive hardened diazo image. The platewas washed with water and placed on an offset printing press, from whichprints of a high quality were obtained. Press life of the plate was20,000 copies.

EXAMPLE 2 The negative working aluminium presensitised plate was coatedand exposed as described in Example 1. The silver emulsion andprotective interlayers were removed by treatment with a solution ofsodium hydroxide (0.5 normal) containing 0.5% w./v. 2-hydroxynaphthalene-3,6-disulphonic acid sodium salt, which at the same timecoupled with the unexposed diazo layer to form an azo dye. There wasthus produced a hardened positive image of the original and also anegative image composed of azo dye. The negative image was removed bygentle rubbing with dilute alkali and the plate washed with water andplaced on an offset printing press. The image was inked-up and from theplate there was obtained positive prints.

EXAMPLE 3 The lithographic plate was prepared and processed as describedin Example 2. In this example, however, the image was protected bylacquering with the resin-solvent mix as described in Example 1. Printswere obtained in the usual way.

EXAMPLE 4 A fairly deeply grained aluminium-alloy plate presensitised bya coating of a formaldehyde-diazo diphenylamine resin was supercoatedwith a 2% W./v. solution of a novolak resin in isopropyl alcohol and theproduct whirled to a smooth dry finish. The plate was again supercoatedwith a high contrast silver halide emulsion which was carefully dried.The plate was exposed to a positive original, and a negative silverimage obtained by the usual processing conditions, then exposed toultra- 'violet light.

The silver emulsion, protective interlayer, unexposed diazo resin layer,were all removed and the image given a protective'lacquer by the use ofa single suspensionemulsified lacquer, which comprised benzylacetate,cyclohexanone, epoxy resins, red pigment gum arabic in aqueous solution,citric acid and nonionic and anionic wetting agents. The plate was thenwashed with water, and retreated with the above lacquer wash mix (thesilver emulsion and protective interlayer dissolve in the organicsolvents, the resins lacquer the ink receptive exposed diazo layer andthe various solvents, citric acid and wetting agents remove theunexposed diazo portions and clean the nonimage areas of the grainedplate).

The plate thus produced was placed on an off-set printing press and verygood quality prints were obtained. The press life of this plate wasabout 50,000 copies.

EXAMPLE 5 A grained aluminium plate suitable for lithography was coatedwith a solution of polyvinyl cinnamate in acetone and allowed to dry,then supercoated with a 2% solution of a novolak resin in isopropanol,by submersion in a dish containing the solution, draining and allowingto air dry. The plate was further supercoated with a high contrastsilver halide emulsion which was carefully dried. The plate was exposedto a positive original and a negative silver image obtained bydevelopment in a metalhydroquinone developer, fixing in a sodiumthiosulphate solution and washing to remove the stabilised silver salts,and dried.

The plate was given a short exposure to ultra-violet light and processedas follows. The silver emulsion and protective interlayer were removedand the image given a protective lacquer by the use of a singlesuspension emulsified lacquer which comprised organic solvents,cyclohexanone and 2-methoxybutylacetate, epoxy resins, gum arabic, redpigment, phosphoric acid and nonionic wetting agents. The plate waswashed with water and retreated with the lacquer. The plate thusproduced was placed on an offset press and good quality prints obtainedfrom it.

EXAMPLE 6 A plate was prepared as in Example 5 except the polyvinylcinnamate was replaced by a solution of partially hydrolysed polyvinylacetate 10% and ammonium dichromate 3.5% in water. The dried coating wassupercoated with novolak resin from isopropanol and the plate coatedwith a silver halide emulsion and processed as previously described.

EXAMPLE 7 A transparent support base of polyethylene terephthalate wassuitably subbed and coated with cellulose acetate and the surfacehydrolysed with potassium hydroxide solution, treated in an acid stopbath, washed and dried.

The support base thus produced was sensitised with the condensationproduct of formaldehyde and 4-diazodiphenylamine using a 2% solution inwater and dried. The plate was supercoated witha novolak resin (2%solution in isopropanol) and dried. It was further coated with a highcontrast silver halide emulsion and dried. The silver halide layer wasexposed to a positive original through the transparent base and thelatent image developed, fixed and washed in the usual way.

The plate was given an overall exposure to ultra-violet light throughthe negative silver layer and the plate processed as follows.

The silver emulsion and protective interlayer were removed by treatmentwith a single suspension emulsified lacquer consisting of cyclohexanone,epoxy resins, red pigment, gum arabic in aqueous solution, citric acidand nonionic and anionic Wetting agents. The plate Was washed with Waterand relacquered with the above mixture, and again washed with water.When placed on an offset printing press good quality prints wereobtained from it.

EXAMPLE '8 A grained aluminium plate suitable for lithography wassensitised by coating with a diazo resin (the condensate of formaldehydewith 4-diazodiphenylamine) from a 2% aqueous solution and dried, thensupercoated with a solution of a novolak resin (2% in isopropanol) andredried.

A stripable layer was coated over the previous layers and was obtainedfrom a 4% solution of a polyvinyl alcohol in water and dried. A highcontrast silver halide emulsion containing a developing agent (e.g.,hydroquinone) was coated thereon and dried. The silver halide layer wasexposed to a positive original and the latent silver image developed inan aqueous alkaline solution and the unexposed portion stabilised with athiocyanate solution containing an aluminium salt, and dried. The platewas given a short exposure to ultra-violet light and the silver halidelayer removed by peeling off the stripable layer. The exposed plate wasprocessed by treating with a combined plate cleaner-lacquer consistingof epoxy resins, cyclohexanone gum arabic in aqueous solution, citricacid, red pigment and anionic and nonionic wetting agents. The plate waswashed with water and placed on an offset printing press. Good qualityprints were obtained from it.

We claim as our invention:

1. A composite presensitised lithographic plate which comprises ahydrophilic-surface support base and coated thereon, in order, a firstlight-sensitive layer which is an adherent ultra violet light-sensitivelayer of the type which when exposed to ultra-violet light through anegative n the exposed areas undergoes a chemical reaction which rendersthe said exposed areas insoluble in a developer liquid whichsubsequently is used to develop the layer by removing the unexposedareas of the layer thus leaving the insoluble areas which form apositive image and exposing the underlying hydrophilic base, the saidinsoluble areas being oleophilic either because the layer is initiallyoleophilic or because on exposure to ultra-violet light the layerbecomes oleophilic, an intermediate protective layer which is an alkalisoluble novolak resin layer and .a second light-sensitive layer which isa silver halide emulsion layer.

2. A composite presensitised lithographic plate according to claim 1wherein the first layer comprises a diazoresin layer.

3. A composite presensitised lithographic plate according to claim 2wherein the diazo-resin layer is the con densation product of4-diazodiphenylamine and formaldehyde.

4. A composite presensitised lithographic plate accord ing to claim 1wherein the first layer comprises a lightsensitive polymer containing anunsaturated acyl group.

5. A composite presensitised lithographic plate according to claim 4wherein the light-sensitive polymer con= taining an unsaturated acylgroup is polyvinyl cinnamate.

6. A composite presensitised plate according to claim 1 wherein thehydrophilic-surface support base is composed of transparent material.

7. A process for the preparation of a printing plate from a compositepresensitised lithographic plate which comprises a hydrophilic-suriacesupport base and coated thereon, in order, a first light-sensitive layerwhich is an adherent ultra-violet light sensitive layer of the typewhich when exposed to ultra-violet light through a negative in theexposed areas undergoes a chemical reaction which renders the saidexposed areas insoluble in a developer liquid which subsequently is usedto develop the layer by removing the unexposed areas of the layer thusleaving the insoluble areas which form a positive image and exposing theunderlying hydrophilic. base, the said insoluble areas being oieophiliceither because the layer is initially oleophilic or because on exposureto ultraviolet light the layer becomes oleophilic, an intermediateprotection layer which is an alkali soluble novolak resin layer and asecond light-sensitive layer which is a silver halide emulsion layer,which comprises exposing the silver halide layer of the presensitisedplate to an original, developing the resultant latent. image,stabilising or fixing out the unexposed silver halide, exposing theplate to ultra-violet light and then removing the silver halide emulsionand the intermediate layer and developing the resultant positive imageof the original in the first layer by removing the unexposedlight-sensitive material therefrom.

8. A process according to claim 7 wherein the first layer comprises adiazo resin, which comprises removing the novolak resin layer and theexposed silver halide layer by treatment with aqueous alkali solutionwhich comprises a diazo cc-iour coupler.

9. A process according to ciaim 7 wherein the first layer compriseseither a diazo resin or a polyvinyl cinnamate, which comprises removingthe novolak resin layer and the exposed silver halide layer anddeveloping the image in the said first layer by treating the exposedplate with a ketone.

10. A process according to claim 9 wherein the ketone is cyclohexanone.

11. A process for the preparation of a printing plate from a compositepresensitised lithographic piate which comprises a transparenthydrophilic-surface support base and coated thereon, in order, a firstlight-sensitive layer which is an adherent ultra-violet light sensitivelayer of the type which when exposed to ultra-violet light through anegative in the exposed areas undergoes a chemical reaction whichrenders the said exposed areas insoluble in a developer liquid whichsubsequently is used to develop the layer by removing the unexposedareas of the layer thus leaving the insoluble areas Which form a psitive image and exposing the underlying hydrophilic base, the saidinsoluble areas being c-ieophilic either because the layer is initiallyoleophilic or because on exposure to ultra-violet light the layerbecomes oleophilic, an intermediate protective layer which is an alkalisoluble novolak resin layer and a second light-sensitive layer which isa silver halide emulsion layer, which comprises exposing the suitablysensitised silver halide emulsion layers of the plate to an originalthrough the noncoated side of the support base with light of wavelengthto which the first layer is not sensitive, developing the resultantsiiver halide image, stabilising or fixing out the unexposed silverhalide, exposing the plate to ultra-violet light on the silver imageside of the base (thus exposing the first layer through the silverimage) and then removing the silver halide emulsion and the intermediatelayer and developing the resultant positive image of the original in thefirst layer by removing the unexposed light-sensitive material there-Irom.

12. A process according to claim 11 wherein the first layer comprises adiazo resin, which comprises removing the novolak resin layer and theexposed silver halide layer by treatment with aqueous alkali Solutionwhich comprises a diazo colour coupler.

13. A process according to claim 11 wherein the first layer compriseseither a diazo resin or a polyvinyl cinnamate, which comprises removingthe novolak resin layer and the exposed silver halide layer anddeveloping the image in the said first layer by treating the exposedplate with a ketone.

14. A process according to claim 13 wherein the ketone is cyclohexanone.

References Cited UNITED STATES PATENTS 1,912,693 6/1933 Cornell 9683X2,140,648 12/1938 Nadeau 959 2,207,388 7/1940 Kujawa 958 3,313,6264/1967 Whitney no 96-33 NORMAN G. TORCHIN, Primary Examiner W. H. LOUIE,JR., Assistant Examiner US. Cl. 9668,

